Interferon induced enzyme activities such as the 2-5A synthetase, the 2',5'-phosphodiesterase, and the 2-5A-dependent ribonuclease are studied with the goal of understanding their role in the action of interferon, the induction of interferon by ds-RNA, and the control of cell growth and differentiation. Analogues of the mediator of interferon action are synthesized in order to define the relationship between oligonucleotide structure and binding to and activation of the 2-5A-dependent endonuclease. The eventual goal is to understand the biological role of the 2-5A system and to explore the potential of exploitation of this system in chemotherapy. Finally, a number of new approaches to pharmacologically active nucleoside analogues are pursued.